Final Update: Cloud Seeding in the Wasatch Mountains

After completing my analysis, I found that 13 of the 15 samples had concentrations below the limit of detection (LoD) of the FAAS instrument which is approximately 1 ppb. While this is great news for the environment, I had initially hoped to correlate concentrations of silver to distance from a cloud seeding generator, but with only 2 determinations, this would not be very statistically relevant. The two samples that registered a signal were Dog Lake (near Clayton Peak) and Lake Martha (near Brighton). There concentrations were calculated to be 0.171 ppm and 0.189 ppm respectively. Overall, my results indicate that current silver concentrations in these high-alpine lakes pose no environmental threat. According to the WHO, daily intake water containing silver at 1 ppm would give a total dose over 70 years that is half the human NOAEL (no observed adverse effect level) dosage of 10 grams. However, it should be noted that ground based generators emit approximately 25 g AgI per hour, and most run continuously throughout the winter months. Thus, it is possible that these silver concentrations will continue to increase, especially as funding and support for cloud seeding programs continues to grow.

One potential source of error in this study arises from the fact that Park City used to be a mining town which profited off its great silver and tin deposits. To prevent detection of possible runoff contamination from these abandoned mines, all samples locations selected are at a higher elevation than these known mines. To eliminate this error entirely, future studies might instead investigate the iodine component of these cloud seeding chemicals using Atomic Emission Spectroscopy since natural iodine deposits are fairly uncommon.

Given the limitations of FAAS, a better technique to study these extremely low silver concentrations would be Graphite Furnace Atomic Spectroscopy (GFAAS) which is accurate well into the ppb range. Unfortunately, I was unable to access this instrument, but this technique would allow to perform a proper statistical analysis like I had originally planned.

Overall, this has been an amazing experience for me. Hiking alone in Utah for a month really tested my self-reliance, but I will never forget the remote locations I was able to see.

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